1. Field of the Invention
The present invention relates to a passive optical network, and in particular to a head-end station for use in such a network.
2. Related Art
The present applicant has developed a bit transport system (BTS) for use in a TPON (telephony on a passive optical network) network. In this bit transport system a head-end station broadcasts time division multiple access (TDMA) frames to all the- terminations on the network. The transmitted frames include both traffic data and control data. Each termination recognises and responds to an appropriately addressed portion of the data in the broadcast frame and ignores the remainder of the frame.
In the upstream direction, each termination transmits data in a predetermined time slot and the data from the different terminations are assembled at the head-end into a TDMA frame of predetermined format.
Typically each TDMA frame includes a header containing bits relating to system functions such as coarse or fine ranging followed by a number of basic frames carrying the traffic data. In the preferred embodiment described below, each basic frame is 2496 bits long, comprising 2352 traffic bits followed by 144 control bits. The control bits may be used by the head-end station, for example, to control the timing and amplitude of the transmissions from the terminations on the network. The appropriate control data is generated by a CPU within the head-end station. On the transmit side of the head-end station it is therefore necessary to assemble the control and traffic data from different sources to form the basic frames. A corresponding function is required for the return data, with it being necessary to split the received frames into traffic and control data.